The Expert Committee on the Diagnosis and Classification of Diabetes
Mellitus. Report of the Expert Committee on the Diagnosis and Classification
of Diabetes Mellitus. Diabetes Care.1999;22(suppl 1):S5-S19.

Context Most antidiabetic agents target only 1 of several underlying causes
of diabetes. The complementary actions of the antidiabetic agents metformin
hydrochloride and rosiglitazone maleate may maintain optimal glycemic control
in patients with type 2 diabetes; therefore, their combined use may be indicated
for patients whose diabetes is poorly controlled by metformin alone.

Objective To evaluate the efficacy of metformin-rosiglitazone therapy in patients
whose type 2 diabetes is inadequately controlled with metformin alone.

Design Randomized, double-blind, placebo-controlled trial from April 1997 and
March 1998.

Setting Thirty-six outpatient centers in the United States.

Patients Three hundred forty-eight patients aged 40 to 80 years with a mean fasting
plasma glucose level of 12.0 mmol/L (216 mg/dL), a mean glycosylated hemoglobin
level of 8.8%, and a mean body mass index of 30.1 kg/m2 were randomized.

Results Glycosylated hemoglobin levels, fasting plasma glucose levels, insulin
sensitivity, and β-cell function improved significantly with metformin-rosiglitazone
therapy in a dose-dependent manner. The mean levels of glycosylated hemoglobin
decreased by 1.0% in the 4 mg/d metformin-rosiglitazone group and by 1.2%
in the 8 mg/d metformin-rosiglitazone group and fasting plasma glucose levels
by 2.2 mmol/L (39.8 mg/dL) and 2.9 mmol/L (52.9 mg/dL) compared with the metformin-placebo
group (P<.001 for all). Of patients receiving
8 mg/d of metformin-rosiglitazone, 28.1% achieved a glycosylated hemoglobin
level of 7% or less. Dose-dependent increases in body weight and total and
low-density lipoprotein cholesterol levels were observed (P<.001 for both rosiglitazone groups vs placebo). The proportion
of patients reporting adverse experiences was comparable across all groups.

Type 2 diabetes is characterized by decreased insulin secretion1,2 and insulin sensitivity in liver,
adipose tissue, and skeletal muscle. Together these abnormalities confound
efforts to treat diabetes because most antidiabetic agents target only 1 underlying
cause of the disease. Approximately 50% of patients treated with monotherapy
require additional therapy to achieve target glycosylated hemoglobin (HbA1c) levels 3 years after diagnosis.3

Rosiglitazone maleate, a member of the thiazolidinedione class of antidiabetic
agents that was recently approved by the US Food and Drug Administration,
targets insulin resistance by binding to the transcription factor peroxisome
proliferator-activated receptor-γ, promoting synthesis of glucose transporters
and activating adipocyte differentiation.4- 6
In contrast, metformin hydrochloride promotes glucose lowering by reducing
hepatic glucose production and gluconeogenesis and by enhancing peripheral
glucose uptake.7- 10

Because metformin and rosiglitazone act through different mechanisms,
their combined use may be indicated in patients whose disease is poorly controlled
with a maintenance dose of metformin. This study evaluated the efficacy and
safety of adding 4 mg/d and 8 mg/d of rosiglitazone maleate to maximal-dosage
of metformin in patients with poorly controlled type 2 diabetes. Combined
efficacy was assessed by comparing the level changes in HbA1c,
fasting plasma glucose (FPG), fructosamine, serum insulin, free fatty acids
(FFA), lipids, lactate, and estimates of insulin sensitivity and β-cell
function (BCF) between combined metformin-rosiglitazone treatment and metformin-placebo
alone.11

METHODS

Study Subjects

To detect a 0.75% absolute difference in HbA1c between treatment
groups, 65 evaluable patients per group would be required to achieve a power
of 95%. Planned enrollment was 280 patients (approximately 93 per group).
Persons between the ages of 40 and 80 years with type 2 diabetes as defined
by the National Diabetes Data Group12 with
FPG concentrations of between 7.8 and 16.7 mmol/L (140 and 300 mg/dL) at screening
and during the placebo-maintenance period while taking 2.5 g/d of metformin
were eligible. All patients demonstrated insulin secretory capacity as determined
by a fasting C-peptide concentration of 0.27 nmol/L (0.8 ng/mL) or more at
screening. Subjects were required to have a body mass index, calculated as
weight in kilograms divided by the square of height in meters, of 22 to 38
and a weight change of no more than 10% between screening and baseline.

Patients were excluded if they had clinically significant renal or hepatic
disease, angina, New York Heart Association Classification class III or IV
cardiac insufficiency, symptomatic diabetic neuropathy, significant clinical
abnormality on electrocardiogram, abnormal laboratory test results (blood
chemistry, hematology, or urinalysis), use of chronic insulin therapy, participated
in any rosiglitazone-related study, or used any investigational drug (excluding
metformin) within 30 days of study (or 5 half-lives of the investigational
drug, if longer than 30 days). Anorectic agents were discontinued at least
30 days before screening. Patients with hyperlipemia, elevated cholesterol
or triglyceride levels, or lipid metabolism disorders were eligible; lipid-lowering
agents were maintained at the same dosage level throughout the study.

Study Design

This multicenter, randomized, double-blind, placebo-controlled trial
was conducted at 36 sites in the United States between April 1997 and March
1998. Before the study, patients discontinued all antihyperglycemic medications,
with the exception of metformin. Metformin dose tolerability was determined
during a 3-week period in which metformin was titrated to 2.5 g/d; afterward,
patients entered a 4-week, single-blind metformin-placebo maintenance period
with a weight-maintenance diet. During this maintenance period, only investigators
were aware that patients were receiving the metformin-placebo treatment. Patients
previously treated with metformin at 2.5 g/d proceeded directly to maintenance;
thus, with the exception of metformin, patients refrained from medication
for a minimum of 4 weeks and a maximum of 7 weeks.

At the end of the maintenance period, patients with inadequate glycemic
control (FPG concentration range, 7.7-16.7 mmol/L [140-300 mg/dL]) were randomly
assigned (1:1:1 ratio) to receive double-blind metformin treatment in 1 of
3 combinations: placebo (control), 4 mg of rosiglitazone, or 8 mg of rosiglitazone
once daily for 26 weeks. Randomization was computer generated with a fixed
block size. No patient, investigator, or sponsor was aware of treatment allocation
until study completion (Figure 1).

This study was conducted in accordance with the Declaration of Helsinki
(as amended, 1989), Title 21 of the US Code of Federal Regulations, and Good
Clinical Practice guidelines. The institutional review board at each center
approved the protocol, and subjects provided informed consent before enrollment.

Estimates of insulin sensitivity determined by homeostasis model assessment
(HOMA-S) and BCF (HOMA-B) were calculated using FPG and immunoreactive insulin
values, or C-peptide levels. HOMA is a mathematical model based on glucose
and insulin interaction in different organs, including the pancreas, liver,
and peripheral tissues.11 HOMA estimates
of BCF and insulin sensitivity were calculated for each participant's FPG
and insulin, or C-peptide levels, and expressed relative to values in a lean,
nondiabetic reference population aged 18 to 25 years.14- 16
HOMA-S determinations of insulin sensitivity or insulin resistance have been
validated by comparison with results of glucose clamp studies,11,14
intravenous glucose tolerance tests,11,15
and continuous infusion of glucose with model assessment.15
The HOMA-B method has been validated by comparison with the intravenous glucose
tolerance test and continuous infusion of glucose model assessment.17 Application of HOMA has also been used in epidemiological
studies.18,19

The primary population for efficacy analysis was the intention-to-treat
population, those with at least 1 value while receiving therapy (last observation
was carried forward in the case of missing data or early withdrawals). Efficacy
and safety parameters were measured at baseline and after 26 weeks of treatment.
Safety parameters were assessed based on week 26 data (without the last observation
carried forward).

Treatment groups were compared using analysis of covariance with terms
for baseline, treatment, and center. The assumptions of the statistical model
were tested before application. The Levene test of heterogeneity across treatments
was applied at a significance level of α = .01. If significant, the
Shapiro-Wilk test of nonnormality (α = .01) was examined. Parametric
analysis or nonparametric analysis was used, depending on results of test
assumptions. If prospectively defined assumptions for parametric analysis
were not met, the Wilcoxon rank sum test was used. Pairwise comparisons to
placebo used Dunnett multiple comparison procedure to maintain a 2-sided .05
significance level within each parameter. The statistical significance of
the within-group change from baseline was tested by a paired t test or a signed rank test. Safety parameters, including clinical
laboratory tests, vital signs, and body weight, were examined using 1-way
analysis of variance. Statistical analyses were performed using statistical
software (SAS/STAT Software, Release 6.12, SAS Institute
Inc, Cary, NC).

RESULTS

Of 443 patients screened, 437 entered the titration and maintenance
period and 348 were randomized to treatment (Figure 1). Most withdrawals were due to failing to meet inclusion
criteria (69.7%). Baseline characteristics were similar among treatment groups
(Table 1). Fifty-eight patients
withdrew before completion of the double-blind phase: 22 from the placebo
group and 18 from the 4-mg/d and 18 from the 8-mg/d rosiglitazone groups.
Most participants withdrew because of adverse experiences or lack of efficacy
(Figure 1).

Glycemic Control

The mean HbA1clevels decreased significantly from baseline
in a dose-dependent fashion in both rosiglitazone groups by 0.56% in the 4-mg/d
and by 0.78% in the 8-mg/d rosiglitazone groups. But the control group experienced
a significant increase in HbA1c levels (0.45%) (Figure 2). Furthermore, both rosiglitazone groups had HbA1c levels lower than those in the control group by 1.0% in the 4-mg/d
and 1.2% in the 8-mg/d rosiglitazone groups. In contrast to results observed
in the control group, the mean HbA1c levels in the rosiglitazone
groups decreased after week 4 and plateaued by week 18 (Figure 3). The percentage who achieved a 1.0% reduction in HbA1c concentrations was 32.8% in the 4-mg/d and 37.3% in the 8-mg/d rosiglitazone
groups and 7.1% in the control group.

Twenty-five (28.1%) of 89 patients taking 8 mg/d of rosiglitazone achieved
the target HbA1c control levels of 7.0%, and 51 patients (57.3%)
in the same group achieved HbA1c levels of 8.0%, or below the American
Diabetes Association action point. Yet only 7.6% of the patients in the control
group achieved HbA1c levels of 7.0% and 35.9% achieved an HbA1c level of 8.0%.

The mean baseline fructosamine levels of 341.73 µmol/L in the
control group increased by 12.3 µmol/L. But in the rosiglitazone groups
the levels decreased by 27.9 µmol/L from 340.9 µmol/L in the 4-mg/d
group and by 36.8 µmol/L from 351.8 µmol/L in the 8-mg/d group
(reference range, 200-278 µmol/L).

Although the mean FPG concentrations did not change significantly in
the control group, they significantly decreased in a dose-dependent order
from baseline in both rosiglitazone groups (1.8 mmol/L [–33.0 mg/dL],
4-mg/d rosiglitazone; –2.7 mmol/L [–48.4 mg/dL], 8-mg/d-rosiglitazone; P<.0001). The mean FPG concentrations in both rosiglitazone
groups also had decreased compared with the control group (−2.2 mmol/L
[−39.8 mg/dL], 4-mg/d rosiglitazone; –2.9 mmol/L [–52.9
mg/dL], 8-mg/d rosiglitazone; P<.0001) (Figure 4). Furthermore, FPG concentrations
in both rosiglitazone groups decreased during the first 4 weeks, plateaued
at 12 to 18 weeks, and remained stable thereafter (Figure 5). Nine patients (7.9%) in the control group, 25 (21.6%)
in the 4-mg/d and 33 (30.0%) in the 8-mg/d rosiglitazone groups achieved FPG
concentrations of less than7.8 mmol/L (140 mg/dL).

Effects on Insulin Sensitivity and BCF

Adding rosiglitazone to maximum doses of metformin significantly increased
HOMA-S values. The median baseline HOMA-S values ranged from 46.6 to 49.0
units. The HOMA-S values increased dose-dependently by 1.7 units in the 4-mg/d
and by 3.8 units in the 8-mg/d rosiglitazone groups compared with the control
group.

The metformin-rosiglitazone combination increased HOMA-B in a dose-dependent
fashion. The median baseline HOMA-B values ranged from 32.5 to 35.8 units
and were significantly increased by 10.3 to 13.7 units in the rosiglitazone
groups compared with the control group.

Other Metabolic Effects

In the control group, the insulin value decreased by 11.05 pmol/L from
a baseline of 118.56 pmol/L after treatment (P =
.03) and in the 4-mg/d and 8-mg/d rosiglitazone groups the insulin values
respectively decreased by 12.98 pmol/L from 124.55 pmol/L (P = .01) and by 31.07 pmol/L from 136.73 pmol/L (P = .14). The C-peptide values respectively decreased by 0.10 nmol/L
from 0.93 nmol/L (P<.001), by 0.07 nmol/L from
0.92 nmol/L (P = .01), and by 0.12 nmol/L from 0.93
nmol/L (P<.001).

Mean total cholesterol-HDL-C, and LDL-C levels from baseline in both
rosiglitazone groups achieved statistically significant increases in all treatment
groups compared with the control group (Table 2). Total cholesterol–HDL-C ratios in the rosiglitazone
groups were not significantly different from those in the control group.

Changes in LDL-C levels were evaluated based on those at baseline. In
that analysis, we identified 2 subgroups: those with levels lower than 3.37
mmol/L (<130 mg/dL) and those at that level or higher. We did not provide P values for any of the subgroups because the values were
not large enough for statistical analyses and because the subgroups were not
randomized, so significance could not be established. In the lower subgroup,
the median baseline LDL-C value increased by 0.13 mmol/L (5 mg/dL) from 2.59
mmol/L (100 mg/dL) in 51 patients in the control group. In both rosiglitazone
groups, the LDL-C values increased by 0.54-mmol/L (21 mg/dL) from a median
baseline value of 2.69 mmol/L (104-mg/dL) in 57 patients taking 4-mg/d and
from 2.64-mmol/L (102 mg/dL) in 60 patients taking 8-mg/d, resulting in medians
that remained below 3.37 (<130 mg/dL) for all 3 treatment groups.

Changes in triglyceride levels also were evaluated based on baseline
values, using 2 subgroups: those with levels lower than 2.26 mmol/L (<200
mg/dL) and those with that level or higher. In the lower subgroup, the median
baseline triglyceride values increased by 0.15 mmol/L (13 mg/dL) from 1.44-mmol/L
(128-mg/dL) in 52 patients in the control group. In the rosiglitazone groups,
the median baseline triglyceride value increased by 0.16 mmol/L (15 mg/dL)
from 1.67 mmol/L (148-mg/dL) in 56 patients taking 4-mg/d and by 0.07 mmol/L
(6 mg/dL) from 1.34-mmol/L (119 mg/dL) in 55 patients taking 8-mg/d. The treatment
values in all groups remained less than 2.25 mmol/L (200 mg/dL).

The percentage of patients with at least 1 adverse event were comparable
among each group (75.2%, 4-mg/d rosiglitazone; 78.2%, 8-mg/d rosiglitazone;
76.7%, control). The most frequently reported adverse events were upper respiratory
tract infection, diarrhea, and headache. One death due to acute myocardial
infarction occurred in the 4-mg/d rosiglitazone group but was judged to be
unrelated to study medication. Serious nonfatal adverse events occurred in
5 (4.3%) of 116 patients in the control group and in 5 (4.2%) of 119 patients
in the 4-mg/d and 5 (4.4%) of 113 patients in the 8-mg/d rosiglitazone groups,
none considered related to study medication.

Symptomatic mild or moderate hypoglycemia was reported by 2 patients
in the control group and by 3 patients in the 4-mg/d and by 5 patients in
the 8-mg/d rosiglitazone groups. No patient required third-party intervention
or hospitalization, but the metformin dose was reduced from 2.5 g/d to 2.0
g/d in 2 patients. No one withdrew because of hypoglycemia, and there were
no biochemically documented instances of FPG levels of less than 2.78-mmol
(<50 mg/dL).

Both rosiglitazone groups experienced small but statistically significant
decreases in hemoglobin and hematocrit levels, which occurred primarily during
the first 12 to 18 weeks of treatment, after which values for both parameters
increased slightly. The mean decreases in hemoglobin levels were −5.0
g/L in the 4-mg/d and –8.0 g/L in the 8-mg/d rosiglitazone groups (P<.0001 for both groups), and mean decreases in hematocrit
were –1.8% in the 4-mg/d and –2.5% in the 8-mg/d rosiglitazone
groups (P<.0001 for both groups). There were no
significant changes in these parameters in the control group. One patient
in each rosiglitazone group withdrew because of anemia, and 1 patient in the
4-mg/d rosiglitazone group with low hemoglobin and hematocrit levels was withdrawn
from the study after week 8 because of evidence of gastrointestinal tract
bleeding, considered by the investigator to be unrelated to the study medication.

There were no significant changes from baseline in vital signs or electrocardiogram
parameters in the rosiglitazone groups compared with the control group. Although
infrequent, edema was observed with greater frequency in the rosiglitazone
groups (2.5%, 4-mg/d; 3.5%, 8-mg/d) than in the control group (0.9%). No one
withdrew due to edema.

Those in the control group experienced a mean decrease in body mass
of 1.2 kg from baseline, but those in the rosiglitazone groups experienced
a mean body mass increase of 0.7 kg in the 4-mg/d and 1.9 kg in the 8-mg/d
rosiglitazone groups (P = .0001 for both groups).
There were no significant differences in waist-to-hip ratios among groups.

No one in the rosiglitazone groups experienced elevations of alanine
aminotransferase (ALT) levels greater than 3 times the upper limit of the
reference range. Mean changes in aspartate aminotransferase (AST), ALT, and
total bilirubin levels were similar in all groups, with a slight decrease
observed in mean ALT (–1.9 U/L, control; –1.9 U/L, 4-mg/d rosiglitazone;
–3.4 U/L, 8-mg/d rosiglitazone). Mean alkaline phosphatase decreased
in all groups (–3.5 U/L, control; –12.0 U/L, 4 mg/d rosiglitazone;
–14.7 U/L, 8-mg/d rosiglitazone); the mean value for all groups was
within the reference range. Two patients in the control group were noted to
have liver function tests for potential clinical concern (>3 times the upper
limit of the reference range) while in treatment. Both completed the study
with elevated transaminase values.

COMMENT

This is the first large, multicenter, clinical trial demonstrating the
efficacy and safety of combined rosiglitazone and metformin treatment in patients
with type 2 diabetes. The combination treatment of metformin and rosiglitazone
significantly reduced HbA1c and FPG concentrations, in a dose-ordered
fashion compared with baseline and with metformin alone. Conversely, treatment
with metformin was associated with significant increases in HbA1c
concentrations, indicating that these agents complement each other to achieve
optimal glycemic control and confirming the clinical utility of metformin
in combination with a thiazolidinedione drug.20

Consistent with the mechanisms of action of metformin and rosiglitazone,
the reductions in FPG concentrations were proportionately smaller than those
observed in HbA1c concentrations. Maximum doses of metformin decrease
hepatic gluconeogenesis, which principally affects FPG concentrations, whereas
rosiglitazone enhances insulin sensitivity at the peripheral level and affects
overall glucose disposal, including postprandial excursions. Because the relative
contribution of postprandial glucose on glycemic control depends on the magnitude
of FPG concentrations,21 rosiglitazone may
have an effect on postprandial hyperglycemia, as demonstrated directly in
a rosiglitazone trial that showed significant improvements in fasting and
postprandial glucose concentrations and excursions.22

The complementary actions of combined metformin and rosiglitazone is
further supported by the effects of rosiglitazone on insulin sensitivity despite
maximum doses of metformin. Rosiglitazone may provide added therapeutic value
by reducing peripheral insulin resistance. While HOMA-S is an indirect method
for determining insulin sensitivity, these results are consistent with glucose-clamp
studies using other thiazolidinedione drugs.23,24

The improvements in HOMA-B with metformin-rosiglitazone treatment (not
observed with metformin alone) were unexpected and introduce an important
potential therapeutic benefit of rosiglitazone. Although the exact mechanism
underlying this improvement remains to be determined, rosiglitazone-mediated
reductions in glucotoxicity25 and lipotoxicity
secondary to elevated concentrations of circulating FFA or both26,27
are candidate mechanisms by which rosiglitazone may improve BCF. The effects
of rosiglitazone on BCF and insulin sensitivity are consistent with its effects
on long-term glycemic control and suggest that it may possibly delay or prevent
disease progression.

Despite significant increases in total cholesterol, HDL-C, and LDL-C
with the metformin-rosiglitazone treatments, the total cholesterol–HDL-C
ratio, which did not change significantly, may be a better predictor of cardiovascular
outcome than either total cholesterol or HDL-C levels alone.28- 30
Since this study was not designed to assess long-term lipid effects, the long-term
significance of these changes is unknown; however, patients with baseline
plasma LDL-C levels lower than 3.37 mmol/L (<130 mg/dL) remained less than
that level after therapy. No significant changes in triglyceride levels were
noted in any treatment group, and segregation of patients into subgroups revealed
nonsignificant increases in patients with baseline triglyceride levels lower
than 2.26 mmol/L (<200 mg/dL). Among patients in the 8-mg/d rosiglitazone
group whose baseline was higher than 2.26 mmol/L (>200 mg/dL), there was a
significant statistical decrease observed (64 mg/dL). The clinical significance
of lipid level changes may be minimal, because lipid-lowering therapy may
be often administered to patients with diabetes irrespective of prior heart
disease history.31,32

Elevated FFA may play a role in the development of insulin resistance,
because it is associated with increased hepatic glucose output33,34
and may contribute to β-cell dysfunction via a lipotoxic effect.26,27 Elevated FFA has also been linked
to endothelial dysfunction and hypertension35,36
and enhanced platelet aggregation and coagulation,37,38
which may increase cardiovascular risk. Therefore metformin-rosiglitazone
treatment was significantly more effective in lowering FFA than the metformin
alone.

The weight gain observed in those receiving metformin-rosiglitazone
treatment may be attributed to increased adipocyte differentiation,39,40 fluid retention,39,41
or increased appetite.42 Despite weight increases,
no significant differences in waist-to-hip ratio among groups were observed,
suggesting that rosiglitazone treatment leads to increased energy storage
in subcutaneous adipose sites that are not associated with increased cardiovascular
risk.43 The small decreases in hemoglobin
and hematocrit levels associated with metformin-rosiglitazone therapy may
relate to plasma volume expansion derived from fluid retention and hemodilution.44

Metformin-rosiglitazone therapy may be a safe alternative therapy to
attain optimal glycemic control where monotherapy has failed because the statistically
significant decreases in lactate levels associated with metformin-rosiglitazone
treatment indicate that rosiglitazone may correct metabolic abnormalities
beyond reducing hyperglycemia, and further suggest differing and complementary
actions of metformin and rosiglitazone; and ALT elevations greater than 3
times the upper limit of the reference range were not observed in either of
the rosiglitazone groups.

In summary, combination metformin-rosiglitazone treatment is effective
and safe in reducing hyperglycemia in patients with type 2 diabetes. In patients
whose fundamental abnormality is insulin resistance, such a combination raises
the exciting possibility of treating diabetes by targeting the underlying
cause of the disease, rather than the traditional approach of stimulating
insulin secretion. Nearly 30% of patients taking the combination therapy achieved
HbA1c levels of 7% or less. This level of glycemic control is 3-fold
greater than what was achieved among those taking metformin alone. Additional
investigation is needed to determine whether this combination will alter the
long-term risk of cardiovascular disease or delay disease progression.

The Expert Committee on the Diagnosis and Classification of Diabetes
Mellitus. Report of the Expert Committee on the Diagnosis and Classification
of Diabetes Mellitus. Diabetes Care.1999;22(suppl 1):S5-S19.